Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$70.61	12.194%	$79.2202	$79.22	$79.20	$79.20
Purchase #2	$78.98	13.337%	$89.5136	$89.51	$89.50	$89.50
Purchase #3	$179.67	11.703%	$200.6968	$200.70	$200.70	$200.70
Purchase #4	$231.31	3.208%	$238.7304	$238.73	$238.75	$238.70
Purchase #5	$51.66	4.415%	$53.9408	$53.94	$53.95	$53.90
Purchase #6	$236.47	5.678%	$249.8968	$249.90	$249.90	$249.90
Purchase #7	$85.48	6.352%	$90.9097	$90.91	$90.90	$90.90
7 purchase totals =	$934.18		$1,002.9083	$1,002.91	$1,002.90	$1,002.80